1. Field of the Invention
The present invention relates to a storage system for optimizing volume capacity among file management computers sharing a storage apparatus, a capacity management method, and a management computer.
2. Description of Related Art
Recently, several patent documents have disclosed an automatic volume expanding technology as a basic function of a storage apparatus. According to Japanese Laid-Open Patent Application No. 2003-15915, in a volume pool containing a plurality of virtual volumes, when a virtual volume is prepared, a physical block is not allocated to the block constituting the virtual volume. When an actual usage request (i.e., write I/O request) is issued, the physical block is allocated to the requested block from the volume pool. By using the automatic volume expanding technology, an administrator becomes free from a capacity expanding operation of the virtual volumes, since what the administrator should operate is only to monitor availability of the volume pool by keeping the capacity of the virtual volume in a sufficiently large size and having the capacity of the volume pool in an appropriate size.
Further, in addition to the volume expanding technology, a volume changing technology is disclosed, which changes volumes stored in the storage apparatus corresponding to a property of a file. For example, according to Japanese Laid-Open Patent Application No. 2006-216070, the storage apparatus classifies the volumes to respective storage tiers called storage classes, in association with a property of a disk constituting the volumes. According to the patent document as mentioned above, in a file system built on the volumes, it is possible to make a file migrate among the different storage classes in association with a dynamic property and a static property of the storage class. Furthermore, it is possible to conceal a change in a file location associated with a file migration, by making a host computer, which refers to the file system through a network, capable of specifying the file by the same file path before and after the file migration.
Moreover, Japanese Laid-Open Patent Application No. 2002006-164211 discloses a concealing technology for concealing a change in a file location caused by the file migration, similarly to Japanese Laid-Open Patent Application No. 2006-216070. The technology described in Japanese Laid-Open Patent Application No. 2006-164211 is different from the technology described in Japanese Laid-Open Patent Application No. 2006-216070, in a point that the latter conceals a file migration among a plurality of computers managing the file systems, while the former conceals the file migration among volumes/file systems with different properties.
For operation and management of the storage apparatus, it is an important and major target to manage performance and capacity of the storage apparatus. Generally, the performance and the capacity of the storage apparatus can be improved by adding storage media such as an HDD (Hard Disk Drive), a tape, and a flash memory. However, addition of the storage media leads to increase in a management cost for an installation area, consuming electric power, and an MTTF (Mean Time To Failure) of the whole storage apparatus as well as an introduction cost of devices. On the other hand, whole capacity and whole performance of the storage apparatus are not used in general. For example, it is told that a usage rate of the capacity for the large storage apparatus, is about 35% in a company.
Because of these factors as mentioned above, if available capacity becomes insufficient in a part of a plurality of volumes provided by the storage apparatus, although the other volumes have the available capacity, addition of the storage media is needed due to insufficient performance and available areas.
There is the same issue in case of a file system built on the volume provided by the storage apparatus. For a general file system, in preparation of the file system, the file system is prepared to have the same capacity size as that of the volume. Then, file data, file management information, and information for managing a usage status of the storage apparatus are stored in the volume. Therefore, if a total size of all files stored in a file system is smaller than the size of that file system, that file system has available capacity. However, if the whole capacity of the volume is already used, the volume has no available capacity. Accordingly, if a file system is short of performance and capacity, addition of the storage media to the file system is needed, even though another file system has available capacity.
Here, if there is available capacity in a file system and the available capacity is made capable of being used by another file system, it is possible to solve a shortage problem of the capacity without adding the storage media, and increase the usage rate of the storage apparatus.
As to a solution of the above mentioned problem, there is a method for reducing the usage rate of the volume by reducing a file system in operation having available capacity. Further, it is possible to solve the shortage problem of the available capacity by allocating the volume capacity not in use, which is not used by the file system, to the file system having no available capacity. However, generally, reduction of the file system is a process to put a heavy load on the storage apparatus due to necessity of data rearrangement in the volume. Therefore, the reduction of the file system should not be conducted frequently.